List of top Questions asked in CBSE CLASS XII

Read the passage carefully and answer the questions that follow.
Passage: The rate of a chemical reaction is expressed either in terms of decrease in the concentration of reactants or increase in the concentration of a product per unit time. Rate of the reaction depends upon the nature of reactants, concentration of reactants, temperature, presence of catalyst, surface area of the reactants and presence of light. Rate of reaction is directly related to the concentration of reactant. Rate law states that the rate of reaction depends upon the concentration terms on which the rate of reaction actually depends, as observed experimentally. The sum of powers of the concentration of the reactants in the Rate law expression is called order of reaction while the number of reacting species taking part in an elementary reaction which must collide simultaneously in order to bring about a chemical reaction is called molecularity of the reaction.
 Answer the following questions:

Phenols undergo electrophilic substitution reactions readily due to the strong activating effect of the OH group attached to the benzene ring. Since the OH group increases the electron density more to the ortho- and para- positions, one of the examples of the aldehyde group being introduced on the aromatic ring of phenol, ortho to the hydroxyl group. This is a general method used for the ortho-formylation of phenols.
Answer the following questions:

Write the IUPAC name of the following complex:
[Co(NH₃)₅(CO₃)]Cl.

Why is a solution of Ni(H₂O)₆²⁺ green while a solution of Ni(CN)₄²⁻ is colourless? (At. No. of Ni = 28)

What type of isomerism is shown by the complex [Co(NH₃)₆][Cr(CN)₆]?

Answer the following:
Low spin tetrahedral complexes are not known.

Answer the following:
Co\(^{2+}\) is easily oxidized to Co\(^{3+}\) in the presence of a strong ligand (At. No. of Co = 27).

Carry out the following conversion
Propanoic acid to Ethane

Carry out the following conversion
Ethanal to But-2-enal

Account for the following:
Conductivity of CH\(_3\)COOH decreases on dilution.

Calculate the potential for half-cell containing 0.01 M K\(_2\)Cr\(_2\)O\(_7\)(aq), 0.01 M Cr\(^{3+}\)(aq), and 1.0 x 10\(^{-4}\) M H\(^+\)(aq).

Write the cell reaction and calculate the e.m.f. of the following cell at 298 K:
\[ \text{Sn}(s) \mid \text{Sn}^{2+} (\text{0.004 M}) \parallel \text{H}^+ (\text{0.02 M}) \mid \text{H}_2 (\text{1 Bar}) \mid \text{Pt}(s) \]
(Given: \( E^\circ_{\text{Sn}^{2+}/\text{Sn}} = -0.14 \, \text{V}, E^\circ_{\text{H}^+/\text{H}_2} = 0.00 \, \text{V} \))

Write the anode and cathode reactions and the overall cell reaction occurring in a lead storage battery during its use.

Account for the following:
On the basis of \( E^\circ \) values, O\(_2\) gas should be liberated at anode but it is Cl\(_2\) gas which is liberated in the electrolysis of aqueous NaCl.

Which vitamin is responsible for the coagulation of blood?

Which one of the following is a disaccharide?
\[ \text{Glucose, Lactose, Amylose, Fructose} \]

How do you convert:
2-Bromobutane to but-2-ene

What is the difference between native protein and denatured protein?

Arrange the following compounds in increasing order of their boiling point:
\[ \text{(CH}_3\text{)}_2\text{NH, CH}_3\text{CH}_2\text{NH}_2, \text{CH}_3\text{CH}_2\text{OH} \]

Give plausible explanation for each of the following:
Aromatic primary amines cannot be prepared by Gabriel Phthalimide synthesis.

How do you convert:
Propene to 1-Iodopropane

Give plausible explanation for each of the following:
Amides are less basic than amines.

Draw the structure of the major monohalo product for each of the following reactions:

Draw the structure of the major monohalo product for each of the following reactions:

How do you convert:
Chlorobenzene to biphenyl